<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
  <title>WebGL - 2D - DrawImage with src rotation and discarded pixels</title>
  <link type="text/css" href="../../resources/webgl-tutorials.css" rel="stylesheet" />
</head>

<body>
  <div id="info">
    <a href="https://webglfundamentals.org/webgl/lessons/zh_cn/webgl-2d-drawimage.html" target="_blank">WebGL -
      二维DrawImage</a>
  </div>
  <canvas id="canvas"></canvas>
</body>
<!-- vertex shader -->
<script id="drawImage-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec2 a_texcoord;

uniform mat4 u_matrix;
uniform mat4 u_textureMatrix;

varying vec2 v_texcoord;

void main() {
   gl_Position = u_matrix * a_position;
   v_texcoord = (u_textureMatrix * vec4(a_texcoord, 0, 1)).xy;
}
</script>
<script id="drawImage-fragment-shader" type="x-shader/x-fragment">
precision mediump float;

varying vec2 v_texcoord;

uniform sampler2D u_texture;

void main() {
  if (v_texcoord.x < 0.0 ||
      v_texcoord.y < 0.0 ||
      v_texcoord.x > 1.0 ||
      v_texcoord.y > 1.0) {
    discard;
  }
  gl_FragColor = texture2D(u_texture, v_texcoord);
}
</script>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See http://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and http://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="../../resources/webgl-utils.js"></script>
<script src="../../resources/m4.js"></script>
<script>
  "use strict";

  function main() {
    // Get A WebGL context
    /** @type {HTMLCanvasElement} */
    var canvas = document.getElementById("canvas");
    var gl = canvas.getContext("webgl");
    if (!gl) {
      return;
    }

    // setup GLSL program
    var program = webglUtils.createProgramFromScripts(gl, ["drawImage-vertex-shader", "drawImage-fragment-shader"]);

    // look up where the vertex data needs to go.
    var positionLocation = gl.getAttribLocation(program, "a_position");
    var texcoordLocation = gl.getAttribLocation(program, "a_texcoord");

    // lookup uniforms
    var matrixLocation = gl.getUniformLocation(program, "u_matrix");
    var textureMatrixLocation = gl.getUniformLocation(program, "u_textureMatrix");
    var textureLocation = gl.getUniformLocation(program, "u_texture");

    // Create a buffer.
    var positionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

    // Put a unit quad in the buffer
    var positions = [
      0, 0,
      0, 1,
      1, 0,
      1, 0,
      0, 1,
      1, 1,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

    // Create a buffer for texture coords
    var texcoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);

    // Put texcoords in the buffer
    var texcoords = [
      0, 0,
      0, 1,
      1, 0,
      1, 0,
      0, 1,
      1, 1,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(texcoords), gl.STATIC_DRAW);

    // creates a texture info { width: w, height: h, texture: tex }
    // The texture will start with 1x1 pixels and be updated
    // when the image has loaded
    function loadImageAndCreateTextureInfo(url) {
      var tex = gl.createTexture();
      gl.bindTexture(gl.TEXTURE_2D, tex);
      // Fill the texture with a 1x1 blue pixel.
      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE,
        new Uint8Array([0, 0, 255, 255]));

      // let's assume all images are not a power of 2
      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
      gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);

      var textureInfo = {
        width: 1,   // we don't know the size until it loads
        height: 1,
        texture: tex,
      };
      var img = new Image();
      img.addEventListener('load', function () {
        textureInfo.width = img.width;
        textureInfo.height = img.height;

        gl.bindTexture(gl.TEXTURE_2D, textureInfo.texture);
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, img);
      });
      img.src = url;

      return textureInfo;
    }

    var textureInfos = [
      loadImageAndCreateTextureInfo('../../resources/star.jpg'),
      loadImageAndCreateTextureInfo('../../resources/leaves.jpg'),
      loadImageAndCreateTextureInfo('../../resources/keyboard.jpg'),
    ];

    var drawInfos = [];
    var numToDraw = 9;
    var speed = 60;
    for (var ii = 0; ii < numToDraw; ++ii) {
      var drawInfo = {
        x: Math.random() * gl.canvas.width,
        y: Math.random() * gl.canvas.height,
        dx: Math.random() > 0.5 ? -1 : 1,
        dy: Math.random() > 0.5 ? -1 : 1,
        xScale: Math.random() * 0.25 + 0.25,
        yScale: Math.random() * 0.25 + 0.25,
        offX: 0,
        offY: 0,
        rotation: Math.random() * Math.PI * 2,
        deltaRotation: (0.5 + Math.random() * 0.5) * (Math.random() > 0.5 ? -1 : 1),
        width: 1,
        height: 1,
        textureInfo: textureInfos[Math.random() * textureInfos.length | 0],
      };
      drawInfos.push(drawInfo);
    }

    function update(deltaTime) {
      drawInfos.forEach(function (drawInfo) {
        drawInfo.x += drawInfo.dx * speed * deltaTime;
        drawInfo.y += drawInfo.dy * speed * deltaTime;
        if (drawInfo.x < 0) {
          drawInfo.dx = 1;
        }
        if (drawInfo.x >= gl.canvas.width) {
          drawInfo.dx = -1;
        }
        if (drawInfo.y < 0) {
          drawInfo.dy = 1;
        }
        if (drawInfo.y >= gl.canvas.height) {
          drawInfo.dy = -1;
        }
        drawInfo.rotation += drawInfo.deltaRotation * deltaTime;
      });
    }

    function draw() {
      webglUtils.resizeCanvasToDisplaySize(gl.canvas);

      // Tell WebGL how to convert from clip space to pixels
      gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

      gl.clear(gl.COLOR_BUFFER_BIT);

      drawInfos.forEach(function (drawInfo) {
        var dstX = drawInfo.x;
        var dstY = drawInfo.y;
        var dstWidth = drawInfo.textureInfo.width * drawInfo.xScale;
        var dstHeight = drawInfo.textureInfo.height * drawInfo.yScale;

        var srcX = drawInfo.textureInfo.width * drawInfo.offX;
        var srcY = drawInfo.textureInfo.height * drawInfo.offY;
        var srcWidth = drawInfo.textureInfo.width * drawInfo.width;
        var srcHeight = drawInfo.textureInfo.height * drawInfo.height;

        drawImage(
          drawInfo.textureInfo.texture,
          drawInfo.textureInfo.width,
          drawInfo.textureInfo.height,
          srcX, srcY, srcWidth, srcHeight,
          dstX, dstY, dstWidth, dstHeight,
          drawInfo.rotation);
      });
    }

    var then = 0;
    function render(time) {
      var now = time * 0.001;
      var deltaTime = Math.min(0.1, now - then);
      then = now;

      update(deltaTime);
      draw();

      requestAnimationFrame(render);
    }
    requestAnimationFrame(render);

    // Unlike images, textures do not have a width and height associated
    // with them so we'll pass in the width and height of the texture
    function drawImage(
      tex, texWidth, texHeight,
      srcX, srcY, srcWidth, srcHeight,
      dstX, dstY, dstWidth, dstHeight,
      srcRotation) {
      if (dstX === undefined) {
        dstX = srcX;
        srcX = 0;
      }
      if (dstY === undefined) {
        dstY = srcY;
        srcY = 0;
      }
      if (srcWidth === undefined) {
        srcWidth = texWidth;
      }
      if (srcHeight === undefined) {
        srcHeight = texHeight;
      }
      if (dstWidth === undefined) {
        dstWidth = srcWidth;
        srcWidth = texWidth;
      }
      if (dstHeight === undefined) {
        dstHeight = srcHeight;
        srcHeight = texHeight;
      }
      if (srcRotation === undefined) {
        srcRotation = 0;
      }

      gl.bindTexture(gl.TEXTURE_2D, tex);

      // Tell WebGL to use our shader program pair
      gl.useProgram(program);

      // Setup the attributes to pull data from our buffers
      gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
      gl.enableVertexAttribArray(positionLocation);
      gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
      gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);
      gl.enableVertexAttribArray(texcoordLocation);
      gl.vertexAttribPointer(texcoordLocation, 2, gl.FLOAT, false, 0, 0);

      // this matirx will convert from pixels to clip space
      var matrix = m4.orthographic(0, gl.canvas.width, gl.canvas.height, 0, -1, 1);

      // this matrix will translate our quad to dstX, dstY
      matrix = m4.translate(matrix, dstX, dstY, 0);

      // this matrix will scale our 1 unit quad
      // from 1 unit to texWidth, texHeight units
      matrix = m4.scale(matrix, dstWidth, dstHeight, 1);

      // Set the matrix.
      gl.uniformMatrix4fv(matrixLocation, false, matrix);

      // just like a 2d projection matrix except in texture space (0 to 1)
      // instead of clip space. This matrix puts us in pixel space.
      var texMatrix = m4.scaling(1 / texWidth, 1 / texHeight, 1);

      // We need to pick a place to rotate around
      // We'll move to the middle, rotate, then move back
      var texMatrix = m4.translate(texMatrix, texWidth * 0.5, texHeight * 0.5, 0);
      var texMatrix = m4.zRotate(texMatrix, srcRotation);
      var texMatrix = m4.translate(texMatrix, texWidth * -0.5, texHeight * -0.5, 0);

      // because were in pixel space
      // the scale and translation are now in pixels
      var texMatrix = m4.translate(texMatrix, srcX, srcY, 0);
      var texMatrix = m4.scale(texMatrix, srcWidth, srcHeight, 1);

      // Set the texture matrix.
      gl.uniformMatrix4fv(textureMatrixLocation, false, texMatrix);

      // Tell the shader to get the texture from texture unit 0
      gl.uniform1i(textureLocation, 0);

      // draw the quad (2 triangles, 6 vertices)
      gl.drawArrays(gl.TRIANGLES, 0, 6);
    }

  }
  main();
</script>

</html>